Electric power distribution systems are commonly exposed to line disturbances, also called transient conditions, current (voltage) transients, and short-circuit conditions. Line disturbances may arise from insulation breakdowns, lightning strikes, or other faults. In the presence of a line disturbance, solid-state transfer switches are used to quickly switch between a failed primary feeder and an alternative secondary feeder, such that utility customers receive uninterrupted power. Solid-state transfer switches may be implemented with Gate Turn-Off Thyristors (GTOs). GTOs have sub-cycle response times. Thus, once a line disturbance is identified, an instantaneous response is possible. The problem is to accurately discriminate between true line disturbances and short term transients.
A conventional magnitude detector is commonly used to detect the loss of a three-phase utility line. A conventional magnitude detector rectifies and filters the three line-to-neutral or line-to-line voltages of the utility line and then compares the value to a threshold. The problem with a rectifier-filter magnitude detector of this type is peak sensitivity. Harmonics and transients significantly affect the peak value. To reject these effects, heavy filtering must be employed. The requisite filtering delays the detection of a line disturbance. Thus, it would be highly desirable to provide a power system switch with the capability of rapidly and accurately assessing system voltage magnitude values indicative of fault conditions.